Identification of "molecular determinants" that regulate bladder cancer (BCa) progression could improve treatment and recurrence monitoring for BCa patients. Hyaluronic acid (HA) is a glycosaminoglycan that promotes tumor metastasis. Hyaluronidase (HAase) is an enzyme that degrades HA into angiogenic fragments. HYAL1 is the major HAase expressed in bladder tumor (BT) cells. It regulates BCa growth and invasion both in vitro and in BT xenografts. While HYAL1 wild type (wt) is enzymatically active and is exclusively expressed in high-grade BCa, 5 HYAL1 variants are enzymatically inactive and expressed in normal and low-grade BCa tissues. In BT tissues, both tumor cells and the stroma produce HA, however, HAS1 type HA-synthase is exclusively expressed in BT cells. The measurement of urinary HA and HAase levels (HA-HAase test) has high accuracy in detecting BCa. This proposal is designed to investigate the therapeutic and prognostic potentials of HYAL1, HYAL1 splice variants, and HAS1 in BCa progression. Furthermore, in a multi-center trial whether the HA-HAase test, either alone or in combination with other urine tests, can be used for monitoring BCa recurrence will be evaluated. To define HYAL1 function(s) in BCa growth and progression, the efficacy of anti-HAase therapy will be tested in BT xenografts, following delivery of HYAL1-antisense cDNA using a viral system or by treatment with a HAase inhibitor. The mechanism of HYAL1 action will be examined by analyzing alterations in cell cycle regulators, matrix degrading enzymes, and angiogenic factors (Aim 1). A possible neutralizing effect of HYAL1 variants on BCa growth and invasion will be examined by cDNA transfection of HYAL1wt expressing BT cells with HYAL1 splice variant cDNAs. Differential expression of HYAL1 variants in BT tissues will be correlated with BT prognosis (Aim 2). HAS1 function in BT growth and progression will be evaluated by transfecting BCa cells which either express or are blocked in HYAL1 production, using HAS1-sense and HAS1-antisense constructs. Expression of HAS1 and its variant (HAS1v) in BT tissues will be correlated with BCa prognosis (Aim 3). In a multi-center trial, the utility of the HA-HAase test, urine cytology, BTA-Stat, NMP22 tests, individually and in combination, will be examined for precision to monitor tumor recurrence in 100 to 150 BCa patients. The results will be compared to clinical findings (Aim 4). The proposed study will reveal the function, therapeutic and/or prognostic potentials of the HA, HYAL1 and related molecules in BT progression. Furthermore, it will establish whether the HA-HAase test or its combination with other tests can precisely monitor BCa recurrence.